Sorry to burst your tits, boys and girls. But this isn't a frozen wave. It's the leading edge of an ice sheet, which is warped due to the friction between itself and the bottom sheet. Wind blows across the top, creating more of a curl. There is no naturally obtainable temperature anywhere on the surface of the earth that can overcome the molecular kinetic energy of a moving wave of water fast enough to freeze it solid mid-action.

Ice forms at the edges of the top of the waterfall, then gradually works its way in. The water flowing over it begins to freeze onto the part formed, and then eventually the entire thing gets covered in ice. It is a long process. Same principle as stalagmites & icicles.

Due to kinetics, unless temperature reaches incredibly low, like record setting low, its impossible to freeze water so suddenly as to capture a wave, its just moving too fast to settle into crystalline form. This is just two glacial sheets pressing up against eachother. The thousand tons of pressure from the ice behind is probably what gave it its smooth surface.